Transient impurity events in JET with the new ITER-like wall
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Citations
Material migration patterns and overview of first surface analysis of the JET ITER-like wall
The influence of an ITER-like wall on disruptions at JET
ELM induced tungsten melting and its impact on tokamak operation
Global erosion and deposition patterns in JET with the ITER-like Wall
Tungsten dust impact on ITER-like plasma edge
References
Recent analysis of key plasma wall interactions issues for ITER
JET ITER-like wall - overview and experimental programme
Modelling of measured tungsten spectra from ASDEX Upgrade and predictions for ITER
Transport mechanisms of metastable and resonance atoms in a gas discharge plasma
Dust in magnetic fusion devices
Related Papers (5)
Plasma operation with an all metal first-wall: Comparison of an ITER-like wall with a carbon wall in JET
The impact of the ITER-like wall at JET on disruptions
ELM-induced transient tungsten melting in the JET divertor
Frequently Asked Questions (15)
Q2. What is the origin of W in limited plasmas?
In limited plasmas, W could originate from W-coated neutral beam shine-through protection tiles as well as from few outer poloidal limiters, recessed inner limiter tiles and restraint ring protection tiles.
Q3. How many events occur in limited plasmas?
The probability of TIEs occurring in limited plasmas is very low (≤ 10 mHz) and only ∼ 7% of all events occur in this configuration.
Q4. What is the effect of disruptions on the redistribution of dust particles?
Following a disruption, light scattered from dust particles (through Mie scattering) that have been heated or ablated by the laser beam is also seen [9].
Q5. What is the likely cause of the events of the divertor?
Since both stainless steel (material of the support structures) and Inconel (support structure of the divertor W mono-block tiles) are made up of Ni, Fe and Cr (althoughin different percentages), dust particles from these parent structures could lead to events of either of these elements.
Q6. What is the reason for the increase in the probability of TIEs occurring in limited plasmas?
Since the normalization of the number of events has been performed over total plasma-time, this increase is probably caused by simple cumulative effects due to higher fraction of total time operated at high input power.
Q7. How many events have been detected by the divertor spectrometer?
Reciprocating probe (RCP) plunges have shown to be the cause of 15 events (< 1%), while arcs at the lower hybrid (LH) antennas are responsible for 7 events (< 0.5%).
Q8. What is the probability of TIEs occurring in a divertor?
Since the horizontal part of the divertor is a deposition zone for material coming from the main chamber, dust which accumulates in this region could partly be the cause of the occurrence of TIEs.
Q9. What is the effect of a MARFE on plasma discharges?
Depending on their composition and size, if such particles reach the plasma core they can perturb it with intense radiation spikes which have been seen to lead to MARFE (stranding for MultifacetedAsymmetric Radiation From the Edge) instabilities or disruptions, especially in long pulse operation [4].
Q10. Why is the probability of TIEs increasing with the fraction of total time spent at higher heating?
Due to the fact that the normalization has been performed over total plasma-time in each specific configuration, the TIE-probability shown in these plots will increase with the fraction of total time spent at higher heating powers.
Q11. How many events have been detected by the HRTS diagnostic?
The number of events detected by the HRTS diagnostic has been seen to decrease constantly during the experimental campaigns with the ILW, dropping of a factor ∼ 4 from the start of the first plasmas to the end of the campaign.
Q12. How is the probability of a TIE normalized?
In order to correctly normalize the event distributions, a database containing the total plasma operation time (in steps of 10 ms) for each geometrical configuration and each correlation quantity listed above has been created.
Q13. What is the effect of disruptions on the dust distribution in the ILW?
Correlation with disruption force reveals that the number of detected dust particles increases strongly with disruption force (figure 3) and confirms the results shown in [10].
Q14. Why is dust production and control a major concern in future tokamaks?
The understanding of dust production and control in future tokamaks such as ITER is a major concern not only for safety reasons and for diagnostic interpretation (see e.g. [1, 2, 3]), but also for reliable plasma operation.
Q15. What is the probability of TIEs occurring in a limited plasma?
Configurations with the outer strike point on vertical tile 7 seem to be less prone to TIE-occurrence than those with the outer strike point on the horizontal tiles 5 or 6 (1.9 mHz vs. 40 − 50 mHz).